We shall complete our experiments on the reverse protection of human cells by mammalian interferons obtained from cultures of heterologous cells that are protectable by human interferons. By means of crossneutralization tests, we shall delineate the antigenic relationships which exist between human interferons and those produced in oher hosts whose cells are to some degree susceptible to the action of human interferons. Antibody responses against the activity of human interferons in homologous and heterologous cultures will be studied in mice subjected to intensive immunization with human interferons. We shall also establish whether or not such antibodies can interfere with the efficacy of human interferon treatment in experimentally infected mice. Efforts will continue to purify and segregate human leukocyte and lymphoblastoid (Namalva) interferons according to structural and antigenic component species. Particularly, we shall seek to compare the Le and F antigenic species from Namalva interferon with Le from leukocyte and F from fibroblast interferon in several heterologous cell systems. Finally, human interferons and their subspecies will be subjected to glycosidic degradation and oxidation by metaperiodate to see whether carbohydrate modification leads to altered antiviral expression in homologous and heterologous cell cultures.